Dbechtel71

Hello I finally took my car out for a ride and it has a bad vibration at above 50 mph it is so bad it shakes my seat. Now I know I had my tires balanced and I repacked the front bearings. What else could it be? Could the drive shaft be out of balance? Thanks

nj67

If it shaking your seat and not the steering wheel it is most likely coming from the rear. I would think it has something to do with one of the rear tires or rims.

Octania

Tires and wheels are the obvious suspects. Balanced is not the same as round. Bad tires can and will vibrate like that. Do you have another set you can swap on? You can move front to rear and see if that helps.

Have a helper drive alongside while their passenger examines your car while it is misbehaving. My car had a bad shake- one day another person was driving my car, I was following on my motorcycle, it was scary- bad cords in the tire made it oval, and it was clearing the ground at speeds over 60. The tire was skipping off the ground.

Dbechtel71

I'll have to try that. God I hope the tires and rims arent bad

droldsmorland

Lil more info. How long has it been sitting. How old are the tires? What have you recently done to it?? Did you look to see if the lug nuts are tight on the studs? Did you crawl under it to inspect the drive shaft, u-joints and other chassis and suspension components for safety and integrity? We cant do this for you on line. Report back your findings and well try to assist you from there.

Dbechtel71

yes I have new u joint in the drive shaft and the lugs are tight.

oldcutlass

Annnnd... has the car been sitting for a long period of time? How old are the tires? Is this something that just started? Have you done anything to the car recently?

Dbechtel71

I've been restoring it for the past three years. They are brand new tires . The car is done I put the new tires on in the late winter so they haven't been on very long

oldcutlass

Check your air pressure and drive it a bit, when tires sit for a while with the car weight on them the get flat spots. If the vibration persists then get them checked for balance and or tread separation.

Dbechtel71

Ok I will check thanks

joesw31

Check my thread at the new defective U-joints
https://classicoldsmobile.com/forums...t-failure.html.

droldsmorland

Before you do anything else double check everything for tightness such as U-joint straps, suspension bushings, etc...
If the "grab-it and wiggle everything test" passes and you find nothing obviously lose then hoist the rear end up, put it safely on jack stands and run it in gear with someone at the wheel and at the brake pedal while you observe from a distance. Please do NOT do this in an enclosed garage. Bring it up to 20-30 mph and see whats hopping around. Stay clear of all moving parts!!!

What brand of tires do you have?

Who did the u-joint replacement?

Note: If you do find the problem please close the loop here so when others do a search the threads complete.

Octania

ruh-roh as Scooby Doo would say

1 - new is not necessarily perfect or even better, verify.

2 - one of my favorite rules- look first at the last thing "fixed"

U-joint retainers can be installed poorly or incorrectly- crud in the grooves, etc. - depending on the technician's skill and level of care. Just went thru this showing my pard how to do U-joints. That circlip has to be seated just right.

broken or worn uj's generally announce their demise with a huge CLUNK between Fwd and Rev gears.